1. Field of the Invention
This invention is directed to a process chamber used to contain inert or reactive process gases for carrying out one or more process steps on a wafer substrate. For example, the process chamber can be used to contain gas reactants for steps such as etching, doping, or growing materials in a process for making integrated electronic, optical or micromechanical devices on the wafer substrate, or for the performance of micromachining, for example. The chamber can also be used to contain an inert gas for a process step that does not require a reactive atmosphere, such as the exposure of a resist layer.
2. Description of the Related Art
Because of their relatively large volume, typically on the order of a few liters or more, previously developed process chambers are generally required to be filled with far more reactant or inert gas than is actually necessary to carry out a particular process step on a wafer substrate. Consequently, such chambers can waste significant amounts of such gases. Also, some gas species are caustic, in which case the relatively large volume of caustic gas required to fill the chamber leads to corrosion of correspondingly large areas of the chamber walls, wafer support surface, piping and other chamber equipment that must be replaced at significant expense. Further, some reactant gas species are toxic, and the accidental release of a large volume of toxic gas from such chambers poses a significant threat to workers in the vicinity of such chamber. Additionally, disposal of large volumes of caustic, toxic or pollutant process gases raises significant health and environmental issues. Furthermore, such large-volume process chambers require significant time to purge and fill with reactant gases, which lowers the wafer throughput of processed wafer substrates attainable with such chambers. It would be desirable to overcome these disadvantages of previous process chambers.
Also of relevance to the subject invention is another problem existing in previous stepper lithography equipment used to pattern devices on a wafer substrate. In the use of such stepper equipment, the wafer stage is repeatedly moved by increments (or in other words `stepped`) relative to lithography projection equipment, and a pattern is exposed on the substrate after each increment of movement. In general, because stage movement relative to the lithography equipment causes the wafer's top surface to move out-of-focus with respect to the lithography equipment, refocusing is necessary after stepping the stage. Such refocusing consumes time and thus lowers the throughput that could otherwise be attained if such refocusing were not necessary. It would be desirable to overcome this disadvantage of previous stepper equipment.